This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Paramagnetic agents are used both as tracers in ESR based imaging and as contrast agents in NMR based imaging to obtain information where they localize in the object being imaged. Imaging using paramagnetic probes applied as tracers in an object of interest in imaging has inherent advantages over NMR. The unique features in ESR based imaging either at a microscopic level or in an in vivo imaging experiment makes it possible to extract important functional information such as local pO2, pH, viscosity etc entities which are significantly more difficult and even challenging in an MRI experiment either at a microscopic or macroscopic level. With the recently available paramagnetic species such as the trityl radicals and solid probes such as LiPc whose spectral properties are optimal for ESR based imaging, it has now become possible at a microscopic level and at an animal level to interrogate at a cellular level: a) subcellular changes in gross redox status changes using redox responsive paramagnetic species;b) sub cellular profiles of oxygen distribution using cell permeable trityl radicals and intra- and extra cellular oxygen gradients using appropriately isotopically labeled spin probes. ACERT will work with the NCI group to examine biological samples from the in vivo experiments where mice receive exposure to radiation in specific organs to such doses that pathologies related to radiation-induced normal tissue fibrosis manifests 4-6 weeks post-radiation.